“We’re seeking to make the most sensitive instrument in the history of mankind,” said Andrew Szentgyorgyi, associate director of the solar, stellar, and planetary sciences division at the Harvard-Smithsonian Center for Astrophysics. “We’re looking to find Earth 2.0.”

On a remote mountain top in Chile's Atacama Desert, one of a new class of what are called “extremely large telescopes” known as the GMT, has been under construction since 2015, and is poised to become the world's largest telescope when it begins early operations in 2021. This giant eye on the cosmos will employ seven specially built mirrors, each with a diameter of nearly 28 feet, making it 10 times more powerful than the 26-year-old Hubble Space Telescope and four times more powerful than Hubble's successor, the James Webb Space Telescope, which it will join in orbit in 2018. The GMT will also use the latest technology to eliminate, as much as possible, atmospheric distortion. Unlike space telescopes, the GMT can be regularly updated.

“It’s really the first time in human history, with the Giant Magellan Telescope, we’ll have the ability to answer the question of whether we’re alone and whether there are other inhabited worlds nearby,” said David Charbonneau, a Harvard professor of astronomy.

The GMT will also house the largest single-piece astronomical mirrors ever made: the 27.6-foot-wide (8.4 meters) concave mirrors must be curved precisely, to within 20 nanometers — the width of a single glass molecule that is currently under constuction at the Steward Observatory at the University of Arizona who's mirror lab is turning out the 20-ton (18 metric tons) glass mirrors.

For the past several years, a group of optical scientists and engineers working at the UA Steward Observatory Mirror Laboratory underneath the UA’s football stadium have been polishing the 8.4-meter-diameter mirror with an unusual, highly asymmetric shape.

By the standards used by optical scientists, the “degree of difficulty” for this mirror is 10 times that of any previous large telescope mirror. The mirror surface matches the desired prescription to a precision of 19 nanometers – so smooth that if it were the size of the continental U.S., the highest mountains would be little more than a half-inch high. This mirror, and six more like it, will form the heart of the GMT, providing more than 380 square meters, or 4,000 square feet, of light-collecting area.

The mirror was cast at the mirror lab from 20 tons of glass, melted in a rotating furnace until it flowed into a honeycomb mold. Once the glass had cooled and the mold material was removed, scientists at the lab used a series of fine abrasives to polish the mirror, checking its figure regularly using a number of precision optical tests.

The mirror has an unconventional shape because it is part of what ultimately will be a single 25-meter (82 feet) optical surface composed of seven circular segments, each 8.4 meters (27½ feet) in diameter.

“We need to be certain the off-axis shape of this mirror, as well as the other six that will be made for GMT, is precisely right, to an accuracy of 1/20 of a wavelength of light,” said Buddy Martin, polishing scientist at the Mirror Lab. “Only then will the seven large mirrors form a single, exquisitely sharp image when they all come together in the telescope in Chile. We have now demonstrated that we can fabricate the mirrors to the required accuracy for the telescope to work as designed.”

Two similar ground megatelescopes with slightly larger fields of view — the Thirty Meter Telescope, which is under construction in Hawaii, and the European Extremely Large Telescope, which is being built in Chile — will use hundreds of tiny mirrors to focus the light of the cosmos. The GMT, on the other hand, will use just seven huge ones (plus one spare) to create the equivalent of an 80-foot (25 m) focusing surface. Four of the mirrors have been cast already, and only one is completely polished.

It also will use the most advanced spectrograph ever built, said Patrick McCarthy, GMT’s project director, It's “the heart and brain of the telescope.”

"I think we're the only one of the giant telescopes that currently has a high-resolution optical spectrograph in its first light, first-generation set of instruments," said Buell Jannuzi, director of the UA Steward Observatory and professor of astronomy. He's particularly excited to see what the high-resolution spectrograph can do, and to image (and eventually measure the spectrum of) the newly discovered planet Proxima b.

Astronomers are hoping the GMT will detect the same kind of oxygen we breathe on Earth (diatomic oxygen, or two atoms of oxygen bonded together) in the atmospheres of other planets outside the solar system. Beyond seeking evidence of life on other planets, the telescope’s unprecedented light-gathering capacity and resolution will help answer some of astronomers’ most fundamental questions: How did the first galaxies form? What is the nature of the dark matter and energy that make up most of space? What will be the fate of the universe?

The scientists are working with colleagues around the world on what they’re calling the Giant Magellan Telescope, a $1 billion device that by 2022 will look out from a mountaintop in the desert of northern Chile toward the far reaches of the universe.

The James Webb, which is expected to cost $8 billion, will allow astronomers to observe parts of the spectrum, particularly invisible infrared energy, that they can’t view from ground-based telescopes.

Harvard has committed $24 million to the project, which involves hundreds of scientists around the world. Other major backers include the University of Texas, the University of Arizona, the Carnegie Institution for Science, the Korea Astronomy and Space Science Institute, the Australian National University, and the University of Sao Paulo in Brazil.

A similar project by a consortium of European nations is working on what it calls the European Extremely Large Telescope, another billion-dollar project slated for Chile, about 500 miles away. That telescope, which is scheduled to begin operations in 2024, will be even larger than the GMT and may be able to view more distant objects at an even higher resolution.

The European telescope uses an experimental technology that relies on about 800 relatively small mirrors. If they work as designed, the telescope should be able to observe stars and planets more quickly, and at farther distances, than the GMT.

“It will use a state-of-the-art technology that has more challenges than the GMT, but also more potential,” said Roberto Tamai, program manager for the European project. “There is certainly competition, but it’s a healthy competition.”

“We think we have an edge,” said McCarthy. “But this competition is a win-win for astronomy," who acknowledged that the European telescope has its advantages, but he said the GMT will boast a wider field of vision, and as a result, lose less light as it scans the universe.